Global Payments, a company that processes card transactions, discovered an unauthorized intrusion into its servers in early March. The company says it "promptly" notified others in the industry. It didn't publicly announce the breach until Friday.

The breach affects all major credit and debit card brands, because Global Payments is one link in the long chain involved in card transactions.

When a customer swipes a credit card, the data is sent to a payment processor like Global Payments, which coordinates the steps involved in authorizing the charge and submitting the transaction details to card networks like Visa (V, Fortune 500) and MasterCard (MA, Fortune 500). It's a quick but complicated process, with lots of players in the mix.

What kind of information was stolen? What can the hackers do with it?

Global Payments (GPN) released a statement late Sunday saying that around 1.5 million card numbers may have been compromised. That's a big breach, but the odds are good that your card wasn't among them. There are more than 1 billion credit and debit cards currently in circulation in the U.S., according to the Nilson Report, an industry trade publication.

Card numbers were stolen, but that's all the thieves got. Cardholder names, addresses and Social Security numbers were not affected, according to Global Payments.

That's good news. Stolen numbers can be used create to fraudulent cards, but they're not enough for full-fledged identity theft.

Global Payments is still investigating how the breach happened. The U.S. Secret Service has launched its own inquiry.

What does this mean for me? Should I be worried?

While the threat of a compromised card is upsetting, customers should sit tight. If your card issuer thinks your account may have been compromised, they'll contact you. Some may need to reissue credit cards or take other steps to contain the damage.

No matter what, you're not liable for unauthorized charges made on your account.

As Visa (V, Fortune 500) put it in a response to the Global Payments debacle: "It's important for U.S. Visa consumer cardholders to know they are protected against fraudulent purchases with Visa's zero liability fraud protection policy, which exceeds federal safeguards. As always, Visa encourages cardholders to regularly monitor their accounts and to notify their issuing financial institution promptly of any unusual activity."